Process for making alkali metal silicates



United States Patent PROCESS FOR MAKING ALKALI lVIETAL SILICATES WilliamT. Gooding, .Ira, Painesville, Ohio, assignor to Diamond Alkali Company,Cleveland, Ohio, at corporation of Delaware No Drawing. ApplicationJanuary 4, 1954 Serial No. 402,163

15 Claims. (Cl. 23-110) of making materials wherein the ratio of, forexample,.

Na O:SiO is between 1.65 to 2.25:1; of especial'interest is material ofthe othosilicate ratio, i. e., 2:1, or approximately so, for example,about 1.852.10Na O: 1sio The invention is concerned also with newproducts made in accordance with the process, The invention contemplatesthat the alkali portion of the compositions under consideration may beany of the alkali metals, including lithium, sodium, potassium, cesium,or rubidium, though of course, the recognized commercial compounds areusually sodium silicates. Hereinafter, reference will be made only tosodium compounds, it being understood that all alkali metals areincluded.

At present, there are several known products described as technicallyanhydrous sodium silicates wherein the ratio of Na O to SiO falls withinthe range contemplated by this invention. Also, various processes areknown for their manufacture. A number of important characteristics havebeen established by the consumers of these materials which are necessaryfor satisfactory performance. Generally, it is quite desirable thatthese materials be readily soluble. Primarily, this is because they areused in such large quantities that the time required for dissolutionbecomes of considerable importance. Another property very desirable inthese materials is high melting point since they are used extensively inhigh temperature lubrication. They lubricate more efficiently in solidphase; accordingly, a significant increase in melting point renders themmore widely usable. Presently known productsmay be said to be generallysatisfactory in these respects, but, as will appear, the products ofthis invention are much improved as to both solubility and melting pointover the known products.

' In addition to the foregoing properties, .it is particularly desirablethat the products be non-deliquescent, and

this invention is especially concerned with this property since productspresently known are generally considered to be unsatisfactory in thisrespect. Because of their deliquescent character, great difliculty isencountered by the producer and the user of known products.

Initially, presentlyknown products are formed as'technically anhydroussub-divided free-flowing materials. However, immediately afterformation, it they are exposed to moist atmosphere, so much water istaken up within a short time that the products become either caked orquite wet and slushy, in either of which forms, of course, they are nottree-flowing solid materials. As illustrative of the conditions that areexperienced in handling these -materials, it is found by exposing threedifferent similar products to the atmosphere, all of which were statedby their manufacturers to be anhydrous orthosilicate, that within thespan of 24 hours, they had increased in Weight from about thirty-threepercent to begun to agglomerate visibly in a few hours and were unsatisfactory for their intended use. Water. absorption at in weight byabout fifty percent was a slushy -mass.

These products were affected by the increase in water content longbefore the passing of 24 hours; they had this rate requires that theproduct be packaged in expensive sealed waterproof containers,substantially 'immediately upon formation, otherwise, the product notonly becomes diflicult to package but its ultimate use 'is seriouslyimpeded. Preferably, packaging is carried out in a dry atmosphere, andshipping and storage containers are water-proof. The consumer must storeopened containers under dry conditions or the contents will absorbsufiicient water to agglomerate. Once the material has agglomerated,great difficulty is encountered in removing it from its package and inbringing it into solutionyfor all practical purposes, dissolution atsuch time may beimpracticable. Thus, products which are subject to thesedisadvantages are of serious concern to both the producer and theconsumer.

It is not believed that others concerned with this problem have.reported its solution priorvto this invention. However, it is a specialadvantage of this. invention that the products produced thereby aregreatly improved as regards the property of deliquescence. Indeed, itmaybe. said that this invention, forpractical purposes, eliminates thetemperatures are sufficiently high to produce avmelted mass, thedisadvantage of corrosive eifects of high temperature melts uponequipment are encountered, which effects necessitate expensive equipmentin order to avoid frequent equipment replacement. Moreover, corrosion ofthe equipment introduces impurities into the product.

Additionally, some of the known processes employ anhydrous caustic asthe ingredient for supplying the Na O content. The useof anhydrouscaustic is to be avoided wherever possible because of its increased costover sodium hydroxide solutions. sults from the expense of dehydrationand special shippingrequirements peculiar to anhydrous caustic. Forexample, itis not possible to ship anhydrous caustic in loose form intank car quantity since, due to its high melting point, it cannotreadily be removed from the.

\ car; instead, it must necessarily be shipped in small steel beshippedin bulk by tank car fitted with internal heat-v drums so that it can behandled conveniently at the point of use. In contrast to this, sodiumhydroxide, which melts at about 65 C., and similar solutions may ingcoils for heating the mass to its liquid form so that itwill flow.

In some of the known processes, the products must be reduced to particlesize at the conclusion of the re-? action because of the fact that asolid cake is produced instead of a discrete mass. This, of course,results in an undesirable additional step in the process.

In contrast to theknown processes, the new process of The processaccording to this invention is a low temperature, process this inventionis free of 'all such difficulties.

Patented June 24, 1958 The increase in cost reand it employs sodiumhydroxide solutions. The reaction results in products composed ofdiscrete crystalline particles that do not require; extensive treatmentthere after to make them useable for their intended purposes.

4 Another advantage which the process of this invention combines withother advantages is that it results veryconsistently in the formation ofcrystalline products. rather closely approaching the orthosilicateratio. Materials of this ratio have considerable market attractiveness.As is well known, it is quite diflicult to causecrystallization of asodium silicate-caustic mixture toa discrete mass having an NagOzSiO,ratio of or near 2: 1. Experience which hasbeen gained heretoforereveals thata liquid mass, fromwhich: crystals of about theorthosilicate ratio might be;

expected to crystallize, quite commonly crystallizes to a product farafield from this ratio; oftentimes, for reasons invention.

The present invention, as indicated above, advances the art to asolutionof this problem. -Sustained operation of the present processconsistently produces a product in which the Na ozsio ratio is betweenabout l.65-2.25:1. Furthermore, where desired, the process may bepracticed in such manner as to provide, consistently, products having aratio of about 1.85 to 2.10:1. Since all of the crystalline materialsthat are formed by the process. are useful, and since products havingthe very useful approximate orthosilicate ratio may be regularlyproduced, the process is especially attractive because of the economicadvantages it affords in supplying consumers who do not require amaterial of a precise ratio. The economic advantage, of course, resultsfrom the extreme simplicity of the process in: contrast to more complexprocesses where the object is to produce a material of the exact orthoratio.

the process eliminates the requirements for precise balancinggotrespective quantities of starting materials since, as will appearhereinafter, the process may be operated within rather. wide limitsprovided that. certain specific preferred conditions are :observed.Moreover, the latitude in starting proportions permitted by the processis not outweighed by the restrictions imposed by preferred conditions ofthe process, because these conditions actually are in themselvesdistinct advantages as compared with the advantages of other knownprocesses.

It has beenfound, according to this invention, that materials having amolecular ratio of about more especially, a ratio of about l.852.lNa O:1SiO mayJbe simply and quickly prepared by combining a sodium silicateof the well-known waterglass family, suitably, a silicate of the formula1Na O:1-3.4SiO,, for example, a material commercially available underthe designation grade 42 silicate, which latter silicate is a Watersolution averaging by weight about thirty-eight and eighttenths percentsolids as lNa O:3.22SiO (weight ratio), and a caustic soda solutionwhich may vary in concentration from about 55% to about 74%, preferably,however, within the range of about 70% to about 73%. The lower limit of55 %j is specified because where concentrations appreciably lower thanthis are employed, the crystalline mass as sought by the inventionbecomes very diflicult to constitute. -For convenience, the startingmaterials are sometimes referred to herein as waterglass and 73% causticsoda, this concentration being specified only because. it is readilyavailable as a commercialproduct.

tempt at explanation be offered in conjunction with this A furtheradvantage which should be mentioned is that waterglass and a causticsoda solution are combined to provide an Na O:SiO ratio of at leastabout 3:1. Actually, the initial Na O:SiO ratio of the starting mixturemay vary from 3:1 to infinityzl. However, this would includecombinations having necessarily impractically large volume requirementsof solutions and correspondingly lower yield of desired crystallinematerial per unit volume of solution.

A more suitable ratio and the preferred range for the practice of theinvention is the combination of waterglass and a caustic soda solutionto provide an Na O:SiO ratio of from about 3.0 to 6.0:1. The

water content of the mixture varies with the concentratwo hours, usuallywithin an hour.

is complete, the crystals and mother liquor are worked to a slurry,centrifuged and then dried at a temperature preftion of the startingmaterials. Mixtures are still more preferred containing Na O and SiO inthe ratio about 3.50-4.5021, since it is found that better size crystalsare formed which are easier to handle; also, it appears that the NaO:SiO ratios of the products from such mixtures are more consistentlymaintained between the desired 1.85-2.l0:l ratio. A preferredformulation is illustrated by a mixture containing, by weight, about9.8% SiO 42.7% Na 0 and 47.5% H O. As may be calculated, the Na;,O:SiOratio in this mixture is 4.22: l.

Suitably, the caustic and sodium silicate solutions are mixed togetherat a temperature above about C. The mixing temperature may beconsiderably higher, for example, 150160 C. or higher. However,temperatures of about 90 to C. are suitable and preferred. After thematerials have been thoroughly mixed, the mixture is cooled to betweenabout 65 and 90 C., preferably, about 75 to 85 C., whereuponcrystallization begins. Crystallization is complete within not more thanabout When crystallization erably above C. 'to a free-flowing,finely-divided mass. During the separation of crystals from motherliquor, a product containing 30% NaOH is produced, and during the dryingsteps, approximately 15% to 20% by weight of water is driven off,providing an ultimate product containing about 12% Water.

In order that the invention may be better understood, several examplesillustrating the invention are provided as follows:

- Example I A liquor is prepared by combining about 151 grams of grade42 silicate with about 199 grams of a 70% sodium hydroxide solution.taining Na O and SiO in the ratio of approximately 3.94:1. Thesematerials are thoroughly mixed at a temperature of about 95 C. and thencooled to about 86 C., at whichtemperature the mixture is held untilcrystallization is complete. The time for crystallization is about onehour. The mass is then stirred to form a slurry of the mother liquor andcrystals and'is thereafter centrifuged and dried. The resultant productis a free-flowing mass of small bodies averaging 1-2 mms. in diameter,

analyzing 2 molecular parts M1 0 to 1 molecular part SiO It is highlysoluble and substantially non-deliquescent.

' Example '11 A liquor is prepared and handled exactly as in ExampleIrexcept that mixing is at about 122 C. and crystallization is allowedto take place by cooling at room tem-' perature. Crystallization takesplace as the temperature drops to below about 90 C. and is completewithin about an hour. The product analyzes 2.02Na- O:1SiO and issubstantiallyidentical to that of Example I.

Example [I] 6'0-65 -C. The .product so formed analyzes about Thisprovides a liquor con-- 1.85Na O:1SiO and exhibits substantially thesame properties as the foregoing products.

, Exampie IV 7 v A liquor is prepared and handled as in the foregoingexamples except that heating is to the boiling point (154 0.), afterwhich the liquor is allowedto cool and crystallize at room temperature.The product analyzes 2.23Na O:lSiO and has about the same properties asthe foregoing products. Rapid cooling ofan identically formed andhandled liquor to about 6 065 C. where crystallization takes place atabout 70-75 C. constant surrounding temperature for about an hour givesasimilar product analyzing 1.87Na O:1SiO

Example V A liquor containing Na o and SiO,, in the ratio of about 3.021is prepared by combining grade 42 silicate and a 70%. caustic sodasolution. The materials are mixed at about 100 C. and, immediatelythereafter, the I mixture is seeded and allowed to crystallize at roomtemperature. After centrifuging and drying, the productanalyzes 1.87NaO:1SiO and is substantially identical to the foregoing products.

Example VI A liquor containing Na O and SiO; in the ratio of about 5.0is prepared by combining grade 42 silicateand a 70% caustic sodasolution. The materials are mixed at about 100 C. and, immediatelythereafter, the mixture is seeded and allowed to crystallize at roomtemperature. After centrifuging and drying, the product analyzes 1.93NaO:1SiO and is substantially identical to the foregoing products.

Example VII A liquor is prepared by combining 200 parts by weight of asilicate solution, containing by weight about 22.05% Na 0, 21.55% Si and56.40% H O, with 234 parts by weight 73% sodium hydroxide solution. Thecombination is accompaniedby mixing and is heated to about 146 C. andthen placed in a constant temperature (73 C.) bath to cool. Crystalsbegin to form after about 20 minutes and are complete a short timelater. The mass is worked to a slurry in the mother liquor and is thencentrifuged. The product analyzes about l.93N O:1SiO- and possessesproperties substantially identical to those or equivalent manner,itbeing intended to cover the invention broadly in whatever form itsprinciple may be scribed by the foregoing, it is thought that somegeneral observations made in the course of study of the process of theinvention will be helpful to those interested in it and these aredescribed in the following paragraphs.

X-ray studies of the products of the invention indicate their chemicalcomposition as being combinations of sodium sesquisilicate andassociated caustic in quantity to provide the additional Na O content. Atypical analysis of the initial product is 49.1% Na 0, 25.4% SiO andwhen dried, the finished product may be stated as 57.1% Na O, 29.4% SiOwith the balance about 12% water, the quantities being by weight.

It appears that systems near 4.0Na O:lSiO and at a total solids contentof about fifty percent give best crystal growth and yield. Moreover,systems of about this initial content tend to give a higher ratioproduct, i. e., about 2Na O: lSiO It does not appear that the mixingrate or the temperature of mixing are critical, but it appears thatbetter crystal growth is obtained if the temperature is adjusted to.

about '125-135 C. just after mixing. 7 Higher tempera-f tures may resultin fine crystals that are difficult to centrif fuge.

Stirring and lization but, again, a mass that is quite fine sometimesforms. 'The liquors usually crystallize well at about ,0 withoutassistance: However, experience with the particular formulationsselected will provide the best technique to follow in these respects.should not be continued a very high ratio product is desired, i.

seeding of the liquor may speed up crystal Generally; ag'itationf' aftercrystallization begins unless i e.," 2.25: 1- or higher. Products havingthe 1.85 -2z10z1 ratio generally; form by stopping agitation whencrystallization starts,

other conditions being observed;

Separation of crystals from the mother liquor in the centrifuge attemperatures under crystallization temperature, especially below about65 C., increase the 'Na O content and, conversely, separation abovecrystallization temperature tends to reduce the Na O content, 'for'example, to as low as about l.65Na O:1SiO Separation at about 65 to 80 C.is generally most satisfactory for producing a product having the nearorthosilicateratio.

Uniform temperature gradient throughout the crystallizing material tendsto provide a more uniform product.

The liquor maybe crystallized in a continuous man-- invention as it isrealized that changes therewithin are possible and it is furtherintendedthat each element recited in any of the following claims is tobe. understood as'referring to all equivalent elements for accomplishingsubstantially the same results in substantially the same utilized.

" What is claimed is:

1.- A process for forming crystalline, sodiumsilicate noncaking in amoist atmosphere, having a melting'point of the order of 2000 F., andhaving an Na O:SiO ratio within the range from approximately 1.65:1 to2.25:1 comprising mixing a sodium hydroxide solution having aconcentration within the range from about 55 to'about 74% NaOH with asodium silicate solution having an Na ozsio ratio within the range fromapproximately 1:1 to 123.4, the sodium silicate and sodium hydroxidebeing in quantities calculated to produce a reaction mixture having anNa O:SiO ratio of at least about 3:1, heating said mixture to at leastabout C., cooling the mixture to a temperature within the range fromabout 65 to about 90 C. and holding the mixture at a temperature withinsaid range until crystallization is substantially complete, separatingthe crystals of high melting point sodium silicate from the mixture, andheata drying the same.

2. A process as claimed in claim 1 wherein said sodium silicate solutionand said sodium hydroxide are combined in proportions to produce an NaO:SiO ratio of between about 3:1 and 6:1.

3. A process as claimed in claim 1 wherein said sodium hydroxidesolution has a concentration of about 70% to 73%.

4. A process as claimed in claim 3 wherein said sodium silicate solutioncomprises Na O and SiO-,, in the ratio of 1 to about 3.22 parts byweight.

5. A process as claimed in claim 4 wherein said sodium silicate solutionand said sodium hydroxide solution are combined in proportions toproduce. an Na Ozsio ratio of about 4:1.

, ratio of 1 to about 3.22 parts by weight.

6. Alprocess for forming crystalline, technically anhysilicatc noncakingin a moist atmosphere,

havingam'elting pointfot the order or 2000 F., and

having an NaO:SiO,"ratio within the range from approximat ely 1.65 :1 to2.2521 comprising mixing asodium hydroxiddsolution having aconcentration Within the range from about, 55. toabout 74%..NaOH with asodium silieate solution having an Na,O:SiO ratio within the ratioofatleastlabout 3:1, heating said mixture to. at

least about 90. C., c o oling the mixture to a temperature within. therange from about 65. to. about 90 C. and holda ing the mixture at atemperature within said range until crystallization is substantiallycomplete, separating. the

crystals of high melting point sodium silicate from the mixture, andheat-drying the same. i l I p 7. A process as claimed in claim 6-whereinsaid sodium silicate solutionQand said sodium hydroxide are combined inproportions to produce an Na ozsiOgrat io of betweenabout 3:1 and 6:1. 78 Aprocess as claimed in claim 6 whereinlsaid sodium. hydroxide solutionhasa concentration ofvabout 70% 107. 1%. P

9. A process as claimed in claim'8 .whereinfsaid sodium. silicatesolution comprises Na O and $10 in the 10. A process as claimed in claim9 wherein s aid sodium silicate solution and said: sodium hydroxidesolution are combined in proportions to produce an Na,O:SiO, ratio ofabout 4: 1.

11. A process as claimed in claim 10 wherein said mixture .is heated tobetween about 100 and 135f C. andlsaid :crystals after separation aredried to a freeflowing particulate mass. 1 p

l2. Aprocess for forming crystalline, alkali metal silicate noncaking ina moist atmosphere, having a melting point of the order of 2000 F., andhaving an alkali metal oxidezSiO, Within the range from approximately1.65 :1

to 2.25:1 comprising mixing an alkali metal hydroxide solution having aconcentration within the range from,

about55-to about 74% NaOH with an alkali. metalggsilicate solutionhaving an alkali metal oxide:SiO; "ratio within therange from.approximately 1:1 to 1:34, the alkali metal silicate and alkali metalhydroxide being in quantities calculated to produce a reaction mixturehaving an alkali metal oxidezSiO-g ratio of at least about 3:1, heatingsaid mixture to at least about 90 C., ,cooling the mixture to atemperature within, the range from V produce a reaction mixture "havingan alkali metal.

about to about'9 0ff C. and holding the mixture at a temperaturewithin'said range until crystallization i's' substantially complete,separatingv the crystals of high melting point alkali metal silicatefromthe mixture, and heat-drying the same.

13. A process for forming crystalline, technically Ian: hydrousalkaliimetal silicate noncaking in a moist at.- mosphere, havingamelting point of the order of 2,000

F.,.and having an. alkali metal oxidezSiO ratio within thera nge fromapproximately 1.65:1 to 2.25:1 compris ing mixing an alkali metalhydroxide solution having a concentration Within. the range from about55 to about 74% NaOH with an alkali metal silicate solution having analkali metal oxidezSiO ratio within the range from approximately 1:1 to1:3.4, the alkali metal silicate and alkali metal hydroxide being inquantities calculated to oxidezSiO ratio of at least about 3:1, heatingsaid mixture to at least about '90" C cooling, the mixture to atemperature within the range from about 65. to about C. and holding themixture at a temperature within said range until crystallization issubstantially complete, separating the crystals of high melting pointalkali metal silicate from the mixture and heat-drying the same.

14. A crystalline alkali metal silicate noncaking in a moist atmosphere,having a melting point of the order of 2000" F., andhaving an alkalimetal oxide:silicon dioxide ratio within the range from approximately1.65:1

to 2.25:1, said silicate having an X-ray diffraction patterncharacteristic of alkali metal sesquisilicate and associated alkalimetalhydroxide.

15. A crystalline sodium silicate noncalting in a moist atmosphere,having a melting pointof the order of 2000 F., and having an Na O:SiOratio within the' range from approximately 1.65 :1 to 2.25:1, saidsilicate having an X-ray diffraction pattern characteristic of sodiumsesquisilicate and associated sodium hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Vail: Soluble Silicates, vol. I, Monograph Series No. 7

116, 1952, pages 30, 32, 112. Reinhold Publishing Co., N. Y. C.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo2,840,456 June 24, 1958 William T, Gooding, Jr,

It is hereby certified that error appears in the-printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5, line 45, after "about strike out "lc93N O:lSIiO and insertinstead l.93Na O:lSiO column 7, line 40, after "oxidezsiO insert ratio 0Signedand sealed this 9th day of September 1958.,

(SEAL) Attest:

KARL Hu AXLINE ROBERT C. WATSON Commissioner of Patents AttcstingOflicer

1. A PROCESS FOR FORMING CRYSTALLINE, SODIUM SILICATE NONCAKING IN AMOIST ATMOSPHERE, HAVING A MELTING POINT OF THE ORDER OF 2000*F., ANDHAVING AN NA2O:SIO2 RATIO WITHIN THE RANGE FROM APPROXIMATELY 1.65:1 TO2.25:1 COMPRISING MIXING A SODIUM HYDROXIDE SOLUTION HAVING ACONCENTRATION WITHIN THE RANGE FROM ABOUT 55 TO ABOUT 74% NAOH WITH ASODIUM SILICATE SOLUTION HAVING AN NA2O:SIO2 RATIO WITHIN THE RANGE FROMAPPROXIMATELY 1:1 TO 1:3.4, THE SODIUM SILICATE AND SODIUM HYDROXIDEBEING IN QUANTITIES CALCULATED TO PRODUCE A REACTION MIXTURE HAVING ANNA2O:SIO2 RATIO OF AT LEAST ABOUT 3:1, HEATING SAID MIXTURE TO AT LEASTABOUT 90*C., COOLING THE MIXTURE TO A TEMPERATURE WITHIN THE RANGE FROMABOUT 65 TO ABOUT 90*C. AND HOLDING THE MIXTURE AT A TEMPERATURE WITHINSAID RANGE UNTIL CRYSTALLIZATION IS SUBSTANTIALLY COMPLETE, SEPARATINGTHE CRYSTALS OF HIGH MELTING POINT SODIUM SILICATE FROM THE MIXTURE, ANDHEATDRYING THE SAME.
 14. A CRYSTALLINE ALKALI METAL SILICATE NONCAKINGIN A MOIST ATMOSPHERE, HAVING A MELTING POINT OF THE ORDER OF 2000*F.,AND HAVING AN ALKALI METAL OXIDE:SILICON DIOXIDE RATIO WITHIN THE RANGEFROM APPROXIMATELY 1.65:1 TO 2.25:1, SAID SILICATE HAVING AN X-RAYDIFFRACTION PATTERN CHARACTERISTIC OF ALKALI METAL SESQUISILICATE ANDASSOCIATED ALKALI METAL HYDROXIDE.